Frames for large pictures and paintings must be particularly strong. Frames constructed of materials such as wood and extruded metals and plastics are very capable of retaining their shape and are suitable to be used to make large frames. However, such materials are expensive and the frames produced thereby are heavy. Sheet metal is, on the other hand, an inexpensive material and also is of light weight construction, but heretofore sheet metal has been reliably usable only in smaller frames where strength is not an important factor.
It has been learned that there are certain advantages to be gained by a construction enabling the picture, the glass pane (if used), and the backing (if used) to be dropped into place from the back as opposed to introducing the elements through one end and then sliding them into place. For example, in a drop-in type frame, filler materials between the backing and the picture are unnecessary. Also, a slide-in frame requires the ends of the side frame members to be sheared to create a mouth for the glass pane, picture, backing, etc. A rear drop-in frame, on the other hand, requires no such sheared ends. However, means heretofore employed for retaining the elements in place for a drop-in type frame have been attachable and detachable with some difficulty and often required the use of a tool. Furthermore, they have not been as strong as necessary to be utilized with large pictures.